1. Field of the Invention
The present invention relates to the preparation of unique polyaminoborazines, to such polyaminoborazines, per se, and to the use of these polymers for the manufacture of ceramic materials and shaped articles based on boron nitride, especially in the form of fibers, films, matrices, coatings, powders and solid parts.
2. Description of the Prior Art
To produce a precursor polymer of ceramic materials based on boron nitride whose pyrolysis behavior and, thus, the yield by weight of boron nitride are improved, it is known to this art to thermally polycondense trifunctional aminoborazines. For example, the thermal polycondensation of various aminoborazines in the presence or in the absence of a heavy amine has been described in EP 0,342,673, GB 2,163,761 and EP 0,384,857.
However, the polyaminoborazines thus produced present the disadvantage of not being homogeneous, namely, such pollers have a polydisperse distribution of their molecular weight, promoting the formation of gels. This formation of gels has the consequence of making it problematical, indeed difficult, to shape these polymers and of producing materials, shaped from these polymers, whose mechanical properties are not satisfactory. By reason of their heterogeneity, these polyaminoborazines can also be partially insoluble and/or can melt at temperatures which are too high to permit the easy shaping thereof.